Detonation arrestors are used in flare lines or relief lines where flammable gases are being vented or discharged for burning. They may also be used in sewage lines and in lines in furnaces, or in any other line in which combustible gases flow. The flammable gases that are being conveyed by the line can sometimes be enriched with oxygen, causing a dangerous condition in which there is potential for an explosion, detonation or other flame front movement in the line. Such an event will be referred to as a flame front. The flame front may travel through the line towards the source of the flammable gases, which may be a storage tank containing flammable gases.
It is therefore highly desirable to have a device in the line that is capable of extinguishing such a flame front as it travels down the line. The device must be designed to extinguish a variety of flame fronts including a continuous or prolonged burn. At the core of such a device is a part that is known as the quenching medium, and various designs have used different such media. The quenching medium is used to extinguish or in other words quench the flame.
Devices presently on the market that are used as detonation arrestors include a device having a quenching medium made of tightly wound expanded metal (aluminum mesh) made by Westech Industrial Ltd. of Sherwood Park, near Edmonton, Canada. The quenching medium includes a core made from fine expanded metal mesh that is rolled into a cylindrical shape, and has its ends cast in liquid steel. Gas passes through the mesh, and while it is useful for stopping detonations, has difficulty withstanding a continuous or prolonged burn. In a continuous or prolonged burn, the flame tends to stabilize on the surface of the cell and the aluminum of the expanded metal mesh tends to melt.
Another device is the Enardo.TM. flame arrestor made by Enardo Manufacturing Co. of Tulsa, Oklahoma. The flame cell of the Enardo flame arrestor is said to be of the wound crimped ribbon type and is said to be custom wrapped to the customer's specifications. A spacer sheet, a sheet of metal formed by crimping, is wrapped with a flat sheet to form the correct diameter cell. This arrestor is said to be designed to separate the flame front into numerous small channels of a preselected dimension which are intended to extinguish the flame front.
In the inventor's issued U.S. Pat. No. 5,145,360, the inventor has proposed a detonation arrestor for connection to a flare line that includes a cell housing defining an interior cavity filled with a particulate quenching medium. First and second flame front diffusors are disposed between the cell housing and the lines to which the arrestor is attached. The particulate quenching medium as described includes a plurality of heat absorbing and corrosion resistant balls, particularly stainless steel balls, and the cell housing includes a deflector ring disposed around the inner circumference of the cavity in the cell housing and extending into the particulate quenching medium. The cell housing also includes a filling pipe for filling the cavity with particulate quenching medium, the deflector ring being located half-way across the entry of the filling pipe into the cavity. In this latter embodiment, the first flame front diffusor may be a steel plate having a diameter greater than the diameter of the outflow line, or may include a particulate quenching medium, which itself is preferably a set of stainless steel balls. The stainless steel balls are retained in place by a wire mesh supported by flat bars with their short faces abutting against the wire mesh. Cross-supports supporting the flame front diffusor may then be oriented at right angles to the flat bars for maximum strength.
In this patent document, the inventor proposes further improvements to the design of the detonation arrestor, including a new design for the heat absorbing section of the detonation arrestor. As compared with the desing shown in the previous application, some of the dimensions have been slightly altered due to design improvements.
The inventor has found that he can do without the flame front diffusor and the wire mesh supporting the quenching medium by using a plurality of closely spaced steel bars stacked parallel to each other on either side of the cell housing. Closely spaced means closer than the expected smallest diameter of the alumina ceramic beads in the case where a particulate quenching medium is used, and preferably much closer than the thickness of the bars themselves. The parallel bars may be helically wound, or planar or curved slightly, and any of various porous media may be used instead of the alumina ceramic beads.
The inventor has found that the steel bars absorb the heat of a flame front and that the beads also absorb the heat and extinguish the flame. A detonation arrestor with the quenching media and the stacked plates provides excellent resistance to a continuous or prolonged burn, with burn times in excess of one hour before experiencing burn back.
In accordance with one aspect of the invention there is therefore provided a detonation arrestor for connection to a line carrying flammable gas, the line having inflow and outflow ends, the detonation arrestor comprising: a cell housing defining an interior cavity in fluid connection with the line; a first heat absorbing section comprised of heat absorbing material disposed across one end of the interior cavity and having channels passing through the heat absorbing material; the heat absorbing material having sufficient heat absorbing capacity to withstand the heat of a continuous or prolonged burn; quenching means adjacent the heat absorbing section for quenching a flame front passing through the cell housing; and means to connect the cell housing to the inflow and outflow ends of the line. The heat absorbing section may be made of stacked plates either plane parallel plates or helically wound, and in the case of helically wound stacked plates, it is preferable that the plates be formed of several layers. The detonation arrestor may include crimped ribbon or like material separating adjacent ones of the stacked plates.
An inspection port is preferably included at each end of the cell housing and the inflow and outflow lines are offset from the center of the cell housing, and set at a lower point to facilitate draining of fluids from the cell housing.
If a sufficiently long section of stacked plates or several sections of stacked plates in series were used, the particulate quenching medium could be removed but this design is difficult to clean and not preferred.